Method and apparatus for handling fines in a briquetting operation



Jan. 7, 1964 AUS D. E. ROH METHOD AND APPARATUS FOR HANDLING FINES IN A BRIQUETTING OPERATION Filed July 10; 1961 APPAQATMS 57AC k FEED 3 \XEK P0740) k/uv 26 l? "U 26 INVENTOR. OO/VAAD 6. 90/1405 BYMGM United States Patent 3,116,996 IVIETHUD AND APPARATUS FOR HANDLING FINES IN A BRIQUETTING OPERATION Donald E. Rohaus, Monroevilie, Pa., assignor to United States Steel Corporation, a corporation of New Jersey Filed July 10, 1961, Ser. No. 122,894 6 Claims. (Cl. 75-3) This invention relates to an improved method and apparatus for handling loose fines which remain after a briquetting operation.

Although my invention has broader application, its principles apply particularly to a hot-briquetting process for iron ore fines. Typically such processes involve heating iron ore fines (for example minus inch or minus A inch) to a temperature of about 1300 to 2100 F. in a rotary kiln or traveling grate for a sufiicient time to expel all moisture, and pressing them into briquettes while they still approach this temperature. When a rolltype briquetting press is used, the pressure required is about 20,000 to 100,000 pounds per linear inch of roll width. 'The resulting briquettes are hard and dense and furnish excellent material for charging to a blast furnace or for open-hearth charge ore. However, there has been a problem in handling loose fines which accompany the briquettes. The usual practice has been to force air over the briquettes and fines and thus cool both to a suitable handling temperature, screen out the fines, and recycle them through the whole process. The cooling air picks up so many particles that it must be cleaned in a cyclone or the like before it can discharge into the atmosphere. Thus this practice necessitates the use of both cyclones and screens, and it wastes sensible heat, #all of which add to the cost.

An object of my invention is to provide a simplified and more efiicient method and apparatus for handling fines in a process of the foregoing type; that is, in which need for cyclones or screens is avoided and sensible heat is conserved.

A more specific object is to provide -a method and apparatus for handling fines in a briquetting process in which an air stream is forced through hot briquettes and fines at a sufiicient velocity to cool the briquettes and pick up most of the fines, and the resulting stream of heated air and hot fines is introduced to the heating chamber at a critical location where sensible heat is effectively utilized.

In the drawing, the single FIGURE is a diagrammatic view of my apparatus with parts broken away.

The drawing shows a heating chamber 10, illustrated as a conventional rotary kiln. I continuously introduce fines (for example minus /2 inch, minus inch or minus /4 inch iron ore) to the left end of chamber through a conventional feeding device 12. The right end of the chamber is equipped with a burner 13 to which I introduce fuel and primary combustion air via pipes 14- and 15 respectively. In this manner, I heat the fines to a suitable briquetting temperature, which in the example of iron ore is about 1500" to 1300 F. I hold the fines at this temperature long enough to drive off all free and combined moisture, which may require about 15 minutes. Waste gases discharge from the left end of the chamber through a conventional flue 16 and stack 17. Hot fines discharge ice continuously from the right end of the chamber through an insulated chute 18 to a conventional briquetting app-aratus :19, illustrated as of the roll-type. This apparatus compacts the fines while still hot under a relatively high pressure and thus forms them into briquettes, as already explained. A series of conveyors 20 and 21 receive the briquettes and accompanying unbriquetted fines and continuously carry them to the entry port 22 at the top of a cooling shaft 23.

In accordance with the present invention, I connect a blower 24 to the lower portion of the cooling shaft 23. and blow cool air through the briquettes and fines therein.

The air stream cools the briquettes to a suitable handling temperature (for example 250 F.), and the cooled briquettes discharge continuously from the bottom of the shaft to suitable handling equipment, such as a conveyor 25. The air also has sufficient velocity to pick up most :of the fines below a predetermined particle size. The velocity required for this purpose of course varies with the specific gravity of the material and the size at which the separation is made. In the example of iron ore fines of a specific gravity of about 4.0 to 5.2, the minimum size a blast furnace can tolerate is about inch, but often it is advantageous to exclude all particles smaller than 4 inch. Hence I adjust the air velocity to pick up minus /s or minus inch particles of the foregoing specific gravity. The velocities required are about as follows:

Particle size Specific gravity of particles /g in. in.

As the air contacts the hot briquettes, it is heated to a temperature about to 300 F. below the temperature at which briquettes enter the shaft. The exact temperature of course varies with the relative air volume and the ambient air temperature. Heated air and entrained fines discharge continuously from the upper portion of the shaft through a pipe 26. The shaft is equipped with a suitable valve 27, such as a star feeder, to prevent escape of air through its entry port 22. Pipe '26 discharges the air and entrained fines into the heating chamber 10 at a critical location a short distance beyond the flame 28 issuing from burner 13. Thus I utilize the heated air as secondary combustion air, while I recycle the fines only through the final portion of the heating chamber and subsequent apparatus. The recycled fines are still at an elevated temperature when they return to the heating chamber, and they are already substantially moisture-free from their previous trip through the chamber. Hence it is advantageous for these fines to bypass the portion of the chamber in which incoming cold fines first are heated and dried. Both the air stream and fines transfer sensible heat from the briquettes back to the heating chamber. It should be pointed out that air from the cooling shaft is not suitable as primary combustion air for burners presently available, for the reason that its large content of entrained fines would clog the burners. Thus my invention is distinguished from the well-known arrangement in which a kiln discharges fused material into a cooling shaft and air is forced through the shaft and used as preheated primary combustion air in the kiln.

As specific examples of my invention, I heated minus inch iron ore in a rotary kiln having a 4 /2 foot inside diameter and a length of 35 feet. I fed the heated ore to a roll-type briquetting press and thus formed it into pillow-shaped briquettes (1 /2 by 1% by A. inches). I transferred the briquettes and unbriquetted fines to a cooling shaft having a 28 inch inside diameter and a height of 14 feet. I introduced air to the shaft and discharged this air to the kiln as already described. The results of three such runs were as follows:

Length of test run, hr 3 3 3 Feed rate to cooling shaft, tons/hr 1. 7 1. 8 1. 85 Air rate to cooling shaft, s.c.f.rn 750 575 650 Ratio, lb. of air to lb. of briquettes and fines 1. 01 0. 73 0. 75 Briquette temperature at press, F 1, 840 1, 680 1, 850 Brique-tte temperature int-o cooling shaft, F. 1, 310 1, 320 1,470 Briquette temperature out of cooling shaft, F. 1 17 235 208 Air inlet temperature, F 55 55 57 Air discharge temperature, 1" 1,150 1,290 1,300

From the foregoing description it is seen that my invention affords a simplified and efficient method and apparatus for cooling briquettes and handling unbriquetted to the disclosure set forth but only by the scope of the appended claims.

I claim:

1. In a briquetting process in which iron oxide fines are heated to an elevated temperature in a heating apparatus, the heated fines are pressed into briquettes accompanied by unbriquetted fines, and the briquettes are cooled, the combination therewith of a method of handling the unbriquetted fines comprising forcing an air stream through the briquettes and unbriquetted fines to cool the briquettes and at a sufficient velocity to pick up and entrain the unbriquetted fines, and discharging the air stream and entrained fines into the heating apparatus at a location at which the air stream serves as preheated secondary combustion air and the entrained fines are recycled only through the final portion of the heating step and subsequent steps and bypass the portion of the heating step in which incoming cold fines first are heated, said location being between the point at which fines leave the heating apparatus and a point in the apparatus beyond which combustion ceases.

2. In a briquetting process in which iron oxide fines feed to a heating chamber and pass continuously therethrough, fuel burns with primary combustion air in said chamber to heat the fines to an elevated temperature, the heated fines from said chamber are pressed into briquettes accompanied by unbriquetted fines, and the briquettes are cooled, the combination therewith of a method of handling the unbriquetted fines comprising forcing an air stream through the briquettes and unbriquetted fines to cool the briquettes and at a sufiicient velocity to pick up and entrain the unbriquetted fines, and discharging the air stream and entrained fines into said heating chamber at a location at which the air stream serves as preheated secondary combustion air and the entrained fines are recycled only through the final portion of the chamber and subsequent steps and bypass the portion of the chamber in which incoming cold fines first are heated, said location being between the point at which fines leave the chamber and a point in the chamber beyond which combustion of the fuel ceases.

3. In a briquetting process in which iron oxide fines feed to one end of a heating chamber and pass continuously therethrough, fuel burns with primary combustion air at the other end of said chamber to heat the fines to an elevated temperature, the heated fines from said chamher are pressed into briquettes accompanied by unbriquetted fines, and the briquettes are cooled, the combination therewith of a method of handling the unbriquetted fines comprising forcing an air stream through the bri quettes and unbriquetted fines to cool the briquettes and at a suificient velocity to pick up and entrain the unbriquetted fines, and dischargiugthe air stream and entrained fines into said heating chamber at a location a short distance beyond the flame produced as the fuel burns with the primary combustion air, thus utilizing the air stream as preheated secondary combustion air and recycling the entrained fines only through the final portion of the cha ber, bypassing the portion of the chamber in which incoming cold fines first are heated, the limit of said distance being the point in the chamber nearer the feed end beyond which combustion of the fuel ceases.

4. In a briquetting process for iron ore fines in which the fines feed to one end of a heating chamber and pass continuously therethrough, fuel burns with primary combustion air at the other end of said chamber to heat the fines to a temperature of about l500 to 1800 F. for a sufiicient time to drive oif free and combined moisture, the fines while still at a temperature approaching that to which they were heated are pressed into briquettes accompanied by unbriquetted fines, and the briquettes are cooled, the combination therewith of a method of handling the unbriquetted fines comprising forcing an air stream through the briquettes and unbriquetted fines to cool the briquettes :and at a suflicient velocity to pick up and entrain the unbriquetted fines, and discharging the air stream and entrained fines into said heating chamber at a location a short distance beyond the flame produced as the fuel burns with the primary combustion air, thus utilizing the air stream as preheated secondary combustion air and recycling the entrained fines only through the final portion of the chamber, bypassing the portion of the chamber in which incoming cold fines first are heated, the limit of said distance being the point in the chamber nearer the feed end beyond which combustion of the fuel ceases.

5. In a briquetting installation which includes a heating chamber, means for feeding fines to one end of said chamber, a burner at the other end of said chamber for burning fuel with primary combustion air, a bn'quetting press, means for continuously transferring heated fines from the burner end of said chamber to said press, and a cooling shaft for receiving briquettes and accompanying unbriquetted fines from said press, the combination therewith of an apparatus for handling the unbriquetted fines comprising means for forcing an air stream through said shaft at a velocity sufficient to pick up and entrain the unbriquetted fines, and means for introducing said air stream and entrained fines to said chamber at a location where the air can serve as preheated secondary combustion air and the fines are recycled only through the latter portion of said chamber and bypass the portion adjacent said feed means, said location being between the point at which fines leave the chamber and a point in the chamber beyond which combustion of the fuel ceases,

6. In a briquetting installation which includes an elongated heating chamber, means for continuously feeding fines to one end of said chamber, a burner at the other end of said chamber, means for introducing fuel and primary combustion air to said burner, whereby the fuel burns with a flame which extends into said chamber, a briquetting press, means for continuously transferring heated fines from the burner end of said chamber to said press, and a cooling shaft for receiving briquettes and accompanying unbriquetted fines from said press, the combination therewith of an apparatus for handling the unbriquetted fines comprising means for forcing an air stream through said shaft at a velocity sufficient to pick up and entrain the unbriquetted fines, and means for intro ducing said air stream and entrained fines to said chamber at a location a short distance beyond the end of flames from said burner where the air can serve as preheated secondary combustion air and the fines are recycled only through the latter portion of said chamber and bypass the portion adjacent said feed means, the limit of said distance being the point in the chamber nearer the feed end beyond which combustion of the fuel ceases.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A BRIQUETTING PROCESS IN WHICH IRON OXIDE FINES ARE HEATED TO AN ELEVATED TEMPERATURE IN A HEATING APPARATUS, THE HEATED FINES ARE PRESSED INTO BRIQUETTES ACCOMPANIED BY UNBRIQUETTED FINES, AND THE BRIQUETTES ARE COOLED, THE COMBINATION THEREWITH OF A METHOD OF HANDLING THE UNBRIQUETTED FINES COMPRISING FORCING AN AIR STREAM THROUGH THE BRIQUETTES AND UNBRIQUETTED FINES TO COOL THE BRIQUETTES AND AT A SUFFICIENT VELOCITY TO PICK UP AND ENTRAIN THE UNBRIQUETTED FINES, AND DISCHARGING THE AIR STREAM AND ENTRAINED FINES INTO THE HEATING APPARATUS AT A LOCATION AT WHICH THE AIR STREAM SERVES AS PREHEATED SECONDARY COMBUSTION AIR AND THE ENTRAINED FINES ARE RECYCLED ONLY THROUGH THE FINAL PORTION OF THE HEATING STEP AND SUBSEQUENT STEPS AND BYPASS THE PORTION OF THE HEATING STEP IN WHICH INCOMING COLD FINES FIRST ARE HEATED, SAID LOCATION BEING BETWEEN THE POINT AT WHICH FINES LEAVE THE HEATING APPARATUS AND A POINT IN THE APPARATUS BEYOND WHICH COMBUSTION CEASES. 